An electrostatic capacitance detection type acceleration sensor which is already known in PTL 1 or PTL 2 is configured with a mass being displaced according to applied acceleration and a detection electrode together with the mass forming electrostatic capacitance. The components may be formed on a silicon substrate having a plurality of layers by repeatedly performing a photolithography technique, an etching technique, and a substrate bonding technique.
In the acceleration sensor of PTL 1, the mass and the detection electrode are formed in a device layer provided so as to have a space on a support substrate. The mass is formed so as to move in a first direction within a plane of the device layer, and the detection electrode is formed so that the electrostatic capacitance formed by the through electrode and the mass is changed according to the displacement of the mass in the first direction. Therefore, the acceleration sensor of PTL 1 can detect acceleration applied in the first direction.
Furthermore, a fixed part which is fixed to the support substrate and supports the mass through a beam which can be displaced in the first direction (x direction) is formed in the central portion of the mass. For this reason, even in the case where distortion occurs in the support substrate due to a change in environment temperature or the like, it is possible to provide an acceleration sensor having small zero-point drift.
In the acceleration sensor of PTL 2, the support substrate and the cap layer are formed in a form of interposing the mass in the upper and lower portions thereof. The mass is configured so as to rotate around the first direction and the second direction, and the detection electrode is provided in the side of the cap layer so that electrostatic capacitance is changed according to the rotation of the mass. In addition, two detection electrodes are arranged so as to be equally spaced from a center of rotation of the mass. Therefore, the mass is rotated according to the acceleration applied in a third direction (z direction) perpendicular to the plane of the support substrate, so that the electrostatic capacitance of the detection electrode which is arranged in the direction where the mass is close to the side of the cap layer is increased. On the contrary, the electrostatic capacitance of the detection electrode which is arranged in the opposite direction symmetrically with respect to the rotational axis of the mass, namely, in the direction where the mass is apart from the cap layer is decreased. By performing differential detection of the electrostatic capacitance from the two through electrodes, an electric signal in proportion to the acceleration applied in the third direction can be obtained.
Furthermore, in the acceleration sensor of PTL 2, the center of rotation of the mass and a center of a cavity configured so the mass is surrounded by the support substrate and the cap layer are allowed to be coincident with each other. Namely, the two detection electrodes are arranged symmetrically with respect to the center of the mass and the center of the cavity. By such arrangement, in the case where distortion occurs in the acceleration sensing unit configured with the support substrate, the mass, the cap layer, and the like due to a change in peripheral temperature and the like, the two detection electrode are uniformly displaced in the direction where through electrodes are closer to or apart from the mass. Therefore, since the changes in electrostatic capacitance of the detection electrodes caused by the distortion are canceled out by the differential detection signals according to application of the acceleration can be extracted. As a result, it is possible to provide an acceleration sensor having small zero-point drift due to a change in mounting factors, environment temperature, and the like.
In PTL 3, the cavity is configured by arranging the support substrate and the cap layer in a form of interposing the mass in the upper and lower portion thereof. In addition, for the purpose of preventing deformation of the cavity caused by external factors such as a change in environment temperature, a plurality of posts are formed to connect a device layer where the support substrate and the mass are formed and the cap layer.
In an acceleration sensor disclosed in PTL 4, as a means of applying an electrical signal to the mass, a conductive structure passing through the support substrate or the cap layer is formed.